Pulp screen plate



July 4, 1933. R W SMH 1,916,393

PULP SCREEN PLATE Filed Sept. 23, 1931 /N VEN TOR @YM/WM Arron/vf: Ys

Patented July 4, 1933 PATENT oFFicE RICHMOND W. SMITH, OF WALPOLE,MASSACHUSETTS PULP SCREEN PLATE Application "filed September 23, 1931.Serial No. 564,561.

My invention yrelates to the paper making industry and particularly toimprove. mentsin devices for screening pulp, paper stock and the like.

5 Heretofore, screens of this type have been made of metal plates,generally bronze, or other non-ferrous metals, having openings ofprecise sizecut therein by sawing or milling. Itis extremely importantthat the screen openings be maintained within a few thousandths of aninch of the size as cut. The life of a metal screen is therefore veryshort due to the rapidity .with which the small but maximum permissibleenlargement of the 35 openings occurs through normal wear. Moreover` theopenings in avmetal plate present comparatively sharp edges and roughsurfaces which tendto catch the passing bers y causing the formation ofstrings which re- 29 sult in slime spots in the finished paper. p

lIt has been proposed to eliminate these difficulties by electroplatinga metal base plate with rubber, thereby covering the sharp edges andrough surfaces of the openings and utilizing the low frictioncoefficient of the rubber, when wet, to increase the capacity of thescreen. minutesize of the openings required and because of the extremelysmall permissible U0 variation in the .size thereof such screens aredifficult to makeand therefore very expensive. Y

Y The principal object of my invention ris to provide a pulp screenplate of rubber having openings of precise dimensions therein and whichcan be constructed at reasonable cost. Another object is to provide ascreen plate having a greater capacity per unit of area and a very muchlonger life than the metal screens now inuse. Another object is toprovide a screen in which the possibility of clogging is reduced to aminimum.

lVith these objects in view, my invention includes the novel elementsand the combinations and arrangements thereof described below andillustrated in the accompanying drawing in which Fig. l is a fragmentaryplan view of my pulp screen plate;

Vir.

Because of the comparativelyl Fig. 2 is an enlarged fragmentary sectionin the plane 2-2 of Fig. l;

Fig. 3 is an enlarged fragmentary section in the plane 3 3 of Fig. l;and

Fig. 4 is a fragmentary perspective view of the screen yon an enlargedscale.

Referring to the drawing, l represents the screen which comprises twoelements, a backing or stiening plate 2, and the rubber ,screen 8 whichare secured together, preferably by cementing and vulcanizing, to form aunitary structure. Y

In making the screen, the metal plate is lirst slotted with a relief sawof thickness somewhat O'reater than the desired width of the finishedslots. This cut does not go en-V tirely through the plate but extendsonly Vto about the depth indicated at 4. The next operation is to cutentirely throughthe plate with a saw only slightly thicker than there-7U quired width of the finished slot, as shown at 5. The metal wallssurrounding the openings are thus free or exposed. f

Since rubber does not vulcanize well to the bronze of which the platesare generally made, before applying the rubber 3 to the plate, the plateis sand blasted and then coated with brass 6 by spraying it thereon in amolten condition as is well understood in the art. This stepispreferably but not necessarily carried out prior tothe cutting throughof the plate. After sand blasting and spray-y ing, the rubber iscemented tothe plate, as shown at 7, and vulcanized thereon. A slottingsaw of the proper size operating through the slots already made in themetal plate is thenused to cut to exact size the screen open# ingsproper in the rubber. These openings, depending upon requirements,generally vary in width between the approximate limits of 0.006 inch and0.090 inch depending upon-conditions such, for example as the nature ofthe pulp and the ycharacter of the sheet required. It is understood ofcourse that all the openings in any one screen should be the same sizeand it is extremely important that the slotsin the rubber be outsquarely and very accurately.V

By reference to Fig. 4 which is an enlarged fragmentary perspective viewof the screen, 100

Vdecrease the size of the openings, but the" rubber should projectslightlylbeyond the edges of the openings in the metal plate as shown inFig. 4. p

The met-al backing'for the screen should be of suliicient thickness toprovide the requisite stability and, as a material therefor, bronze ispreferred. The rubberscreen itself may be about 116 inch thick and of adensity around twenty plastomcter although it is to be understood thatthe invention is in no sense limited in these respects.

Screens made according to my invention arc not only substantiallyinore'eliicient than all metal screens but are extremely resistant towear. The life of such a screen is indefinitely long and cannot beaccurately estimated at this time. One specimen which has been inoperation over a year indicates no enlargement of the openings. On theother hand a comparative test of a rubber and bronze screen,respectively, extending'over a period of two months showed noenlargement whatever in the openings in the rubber screen whereas theopenings in a bronze screen showed an average enlargement of 0.004 inch.

While I have described my invention in its preferred embodiment it is tobe understood that thewords which I have used are words of descriptionandnot of limitation and that changes within the scope of the appendedclaims may be made without departing from the true scope and spirit ofmy invention in its broader aspects.

What I claim isy 1. A pulp screen plate comprising a layer of rubberhaving openings therein, and a stilening plate substantially coextensivewith the perf-orate portion of said rubber and having openings thereinycommunicating withthe openings in said rubber but slightly larger insize. y

2. A pulp screen plate comprising'a rigid metal plate having a layer ofrubber'secured to one side thereof to orm a unitary struc` ture andprovided with a multiplicity of passages extending therethrough.

V3. A pulp screen plate comprising a rigid metal plate having a layer ofrubber secured to oneV side thereof to form a unitarystruci ture andprovided with a multiplicity of pas sages extending therethrough; saidpassages being of larger cross sectional area in the metal than in therubber.

4L. In a pulp screen plate, the combination with a rubber plate havingslotted openings therein forming the screen proper, of means on one sidethereof for stiffening said plate around the edges of said openings toprevent deformation under liquid pressure.

A pulp screen plate comprising a metal base plate having slottedopenings therein of substantially greater cross sectional area at oneside of said plate than at the other, and a rubber plate vulcanizedthereon and having slottedopenings therein communicating with but ofsmaller cross sectional area thanthe vminimum area of the openings insaid plate.

6. A pulp screen plate comprisin a rigid plate of corrosion resistantmetal aving a layer of brass thereon and provided wlth slotted passagestherethrough, and a rubber plate vulcanized on said brass and providedwith slotted passages communicating with the passages in said metalplate.

7. A pulp screen plate comprising a metal plate having slotted openingstherein provided with free` edges, and a rubber facing connected to saidplate ;v said facing having slotted openings therein the walls surround`ing which overlie and 'project slightly beyond the wallssurroundin'githe openings in the plate.

8. Ay pulp screen plate comprisinga metal plate and a rubber platesecured together to form a unitary structure, and provided-with amultiplicity of slotted passages therethrough; the side walls of saidpassages through the metal being exposed and splayed outwardly. u

9. -A pulp screen plate comprising a metal plate and a rubber platevulcanized together to form a unitary structure, and provided with amultiplicity of slotted passages there through; the side walls of saidpassages through the rubber portion of the structure being parallel andin precise spaced relation and 4theside walls of said passages throughthe metal portion of the structure being exposed and splayed outwardly.u

l0. A pulp screen plate comprising a metal plate having a layer ofrubber on one side thereof and provided with a mutiplicity of slottedpassages therethrough, the walls surrounding the openings in the metalbeing exposed, the edges of the openings to said passages on the rubberside of said screen being square and sharp whereby openings of a precisewidth are defined.

11. The method of making a pulp screen plate which comprises cuttingslotted openings in a metal plate, cementing a sheet of rubber to saidplate, and thereafter cutting slotted openings in said sheetcommunicating with the openings in said plate.

l2. The method of making a pulp screen face of the plate than the other,Vulcanizing a layer of rubber over the surface of said plate having theopenings of lesser Width therein, and thereafter forming in said rubber,slots of precise, predetermined but smaller size than the plate slots bycutting the rubber through the passages in said plate.

RICHMOND W. SMITH.

